Oats are well adapted to grow in damp, cooler climates, such as our own, and are often regarded, with good justification, as a low-input crop. However, as with other cereals, oats can suffer from a wide range of fungal diseases. Some of these diseases only affect oats, whereas other diseases have a broad host range and affect a number of cereal crops including oats.
Fungal diseases which can affect oats include powdery mildew, crown rust, stem rust, leaf blotch, red leather leaf, eyespot and fusarium. However, the most prevalent diseases of oat crops in Ireland are powdery mildew, crown rust and fusarium, with red leather leaf being prevalent in some years.
There is also a species of take-all which can affect oats, although infections are rare and usually only occur where oats are grown continuously.
This article looks at the main individual diseases and their potential significance.
Little specific work has ever been done on disease control of oats. Little specific work has ever been done on disease control of oats.
Powdery Mildew
Infections of powdery mildew often occur in cool wet conditions and oats are attacked by a specialised form which does not attack other cereal species.
Leaves are generally infected, although any parts of the plant which contain chlorophyll can be attacked. Symptoms are similar to other cereal species, showing grey-white colonies of mycelia. The disease can sometimes produce a sparse covering of hyphae over the whole leaf.
On occasions, mildew infection can cause a hypersensitive reaction on the leaf, which produces reddish-brown patches, but such a reaction is more common in more resistant varieties. The disease can occur at any time during the growing season, although it is sometimes less prevalent towards grain fill if high temperatures limit its development. Mildew infection can result in yield losses of up to 20% to 30%.
Crown Rust
Oats can be infected with stem rust, but the most common form of rust encountered is crown rust. The crown rust fungus only infects oats and does not cross to other cereals.
The fungus generally affects the leaves and stem sheaths and appears initially as bright orange pustules. Severe infections can sometimes result in lesions on the oat panicle. Later in the season, the pustules may turn black.
Crown rust can be a very significant disease of oats and cause severe defoliation.Crown rust can be a very significant disease of oats and cause severe defoliation.
Crown rust development is favoured by warm and wet or humid conditions and, for this reason, crown rust epidemics typically occur later in the growing season in June and July. Yield losses of up to 10% to 20% can occur as a result of crown rust.
Fusarium
Oats can be infected by fusarium. As in other cereals, the major affect is head blight. Infection often occurs after panicle emergence, but before flowering, and this can result in both yield loss and mycotoxin build-up in grain.
Symptoms are not always visible, but bleached spikelets are the general indicator. However, bleached or empty spikelets can also be a consequence of the plant aborting grain sites when conditions appear unfavourable for grain fill.
Fusarium can sometimes attack the leaf sheath in the autumn to give it a dead and watery appearance, which results in the production of a senesced V at the base of the leaf where it joins the sheath. When this happens, it can sometimes result in the production of horizontal cuts or nicks in the stem during stem extension.
Red Leather Leaf
This disease was first reported in Ireland in 1988, when severe symptoms were widespread on autumn-sown crops.
The disease is characterised by grey-brown elliptical lesions, developing into light-grey eyespots surrounded by dark borders. Plants are stunted and show reddish-brown foliar pigmentation extending beyond the lesions.
However, in general, this is a relatively minor disease of oats and is not widespread in most years. The symptoms of the disease (red pigmentation of leaves) are often confused with the symptoms of other disorders and stresses, as oat leaves tend to turn red in response to a wide variety of stresses.
Research
In general, research on disease control in oats is limited compared with wheat and barley. However, early research conducted in the United Kingdom established that significant yield responses to fungicide programmes only occurred where significant foliar disease symptoms were present. In other words, yield was not affected when disease was not present.
Similarly, Teagasc trials in recent years found no response to fungicide programmes in some years and in some areas.
The 2015 growing season is a good example. Two fungicide trials were conducted in 2015 on autumn-sown Husky crops in both Knockbeg (near Carlow) and in Cork.
At the Knockbeg site, disease did not develop until quite late in the growing season when some mildew appeared in late June. As a result, there was no yield response to any of the fungicide programmes included in the trial in Knockbeg.
There was more disease development at the Cork site in that year and this resulted in a 0.4t/ha yield difference between no fungicide and a full fungicide programme.
However, one fungicide spray applied early in the growing season provided the same yield response as a full fungicide programme with four sprays.
In contrast, 2017 was a very different year for disease control in oats. High levels of mildew were evident from early in the growing season and there were blotching symptoms present, particularly on crops of Husky.
The exact cause of these blotching symptoms remains uncertain, but they may have been the result of a form of septoria infection specific to oats Septoria avenae.
In 2017, there was a large response to fungicide application. The difference in yield between a treatment which received a full fungicide programme and a treatment which received no fungicide was 1.5t/ha, similar to the yield response which could be expected from fungicide application to wheat and barley crops.
Thus, for years with high disease pressure, a full prophylactic fungicide programme with fungicide applications at GS30/31, GS32 and GS55 may be necessary to protect yield potential in autumn-sown oats, particularly for disease-sensitive varieties such as Barra.
In such years, trials around the country have shown consistently big responses to the use of fungicides on oats, with some of the new SDHI chemistry showing considerable benefits over older chemistry in terms of yield and quality.
For spring-sown crops, two fungicide applications may be sufficient, although much will depend on the timing of infection. However, in years with low disease pressure, the yield potential can be delivered with a lower number of fungicide applications.
In such years, protective mildewicides such as Talius may have a role in preventing subsequent mildew infections. However, very frequent use of such fungicides will increase the risk of resistance development to these active ingredients in the mildew population.
Where disease pressure is present but not severe, UK research on oats has shown that reduced fungicide rates can be as effective as full rates.
Variety choice also has a role in disease control, particularly for mildew, as the varieties on the current spring and winter recommended lists have similar resistance to crown rust.
In a spring oat trial conducted in Oak Park in 2017, with high levels of mildew but low levels of rust, yields of Binary were reduced by 18% but yields of Barra were reduced by 38% when no fungicide was applied.
Some growers may be restricted in their choice of variety by their contract and may have to use a variety with lower disease resistance. With such varieties, closer monitoring of disease pressure will be needed in order to ensure that the optimal fungicide strategy is employed to maximise yield potential.
There are a number of potential diseases that can attack oat crops, but mildew and crown rust tend to be the most damaging.Research has not always found a benefit from fungicide application.Oat plants are very prone to blotching and purple discolouration, but this is not always a yield issue.
Oats are well adapted to grow in damp, cooler climates, such as our own, and are often regarded, with good justification, as a low-input crop. However, as with other cereals, oats can suffer from a wide range of fungal diseases. Some of these diseases only affect oats, whereas other diseases have a broad host range and affect a number of cereal crops including oats.
Fungal diseases which can affect oats include powdery mildew, crown rust, stem rust, leaf blotch, red leather leaf, eyespot and fusarium. However, the most prevalent diseases of oat crops in Ireland are powdery mildew, crown rust and fusarium, with red leather leaf being prevalent in some years.
There is also a species of take-all which can affect oats, although infections are rare and usually only occur where oats are grown continuously.
This article looks at the main individual diseases and their potential significance.
Little specific work has ever been done on disease control of oats. Little specific work has ever been done on disease control of oats.
Powdery Mildew
Infections of powdery mildew often occur in cool wet conditions and oats are attacked by a specialised form which does not attack other cereal species.
Leaves are generally infected, although any parts of the plant which contain chlorophyll can be attacked. Symptoms are similar to other cereal species, showing grey-white colonies of mycelia. The disease can sometimes produce a sparse covering of hyphae over the whole leaf.
On occasions, mildew infection can cause a hypersensitive reaction on the leaf, which produces reddish-brown patches, but such a reaction is more common in more resistant varieties. The disease can occur at any time during the growing season, although it is sometimes less prevalent towards grain fill if high temperatures limit its development. Mildew infection can result in yield losses of up to 20% to 30%.
Crown Rust
Oats can be infected with stem rust, but the most common form of rust encountered is crown rust. The crown rust fungus only infects oats and does not cross to other cereals.
The fungus generally affects the leaves and stem sheaths and appears initially as bright orange pustules. Severe infections can sometimes result in lesions on the oat panicle. Later in the season, the pustules may turn black.
Crown rust can be a very significant disease of oats and cause severe defoliation.Crown rust can be a very significant disease of oats and cause severe defoliation.
Crown rust development is favoured by warm and wet or humid conditions and, for this reason, crown rust epidemics typically occur later in the growing season in June and July. Yield losses of up to 10% to 20% can occur as a result of crown rust.
Fusarium
Oats can be infected by fusarium. As in other cereals, the major affect is head blight. Infection often occurs after panicle emergence, but before flowering, and this can result in both yield loss and mycotoxin build-up in grain.
Symptoms are not always visible, but bleached spikelets are the general indicator. However, bleached or empty spikelets can also be a consequence of the plant aborting grain sites when conditions appear unfavourable for grain fill.
Fusarium can sometimes attack the leaf sheath in the autumn to give it a dead and watery appearance, which results in the production of a senesced V at the base of the leaf where it joins the sheath. When this happens, it can sometimes result in the production of horizontal cuts or nicks in the stem during stem extension.
Red Leather Leaf
This disease was first reported in Ireland in 1988, when severe symptoms were widespread on autumn-sown crops.
The disease is characterised by grey-brown elliptical lesions, developing into light-grey eyespots surrounded by dark borders. Plants are stunted and show reddish-brown foliar pigmentation extending beyond the lesions.
However, in general, this is a relatively minor disease of oats and is not widespread in most years. The symptoms of the disease (red pigmentation of leaves) are often confused with the symptoms of other disorders and stresses, as oat leaves tend to turn red in response to a wide variety of stresses.
Research
In general, research on disease control in oats is limited compared with wheat and barley. However, early research conducted in the United Kingdom established that significant yield responses to fungicide programmes only occurred where significant foliar disease symptoms were present. In other words, yield was not affected when disease was not present.
Similarly, Teagasc trials in recent years found no response to fungicide programmes in some years and in some areas.
The 2015 growing season is a good example. Two fungicide trials were conducted in 2015 on autumn-sown Husky crops in both Knockbeg (near Carlow) and in Cork.
At the Knockbeg site, disease did not develop until quite late in the growing season when some mildew appeared in late June. As a result, there was no yield response to any of the fungicide programmes included in the trial in Knockbeg.
There was more disease development at the Cork site in that year and this resulted in a 0.4t/ha yield difference between no fungicide and a full fungicide programme.
However, one fungicide spray applied early in the growing season provided the same yield response as a full fungicide programme with four sprays.
In contrast, 2017 was a very different year for disease control in oats. High levels of mildew were evident from early in the growing season and there were blotching symptoms present, particularly on crops of Husky.
The exact cause of these blotching symptoms remains uncertain, but they may have been the result of a form of septoria infection specific to oats Septoria avenae.
In 2017, there was a large response to fungicide application. The difference in yield between a treatment which received a full fungicide programme and a treatment which received no fungicide was 1.5t/ha, similar to the yield response which could be expected from fungicide application to wheat and barley crops.
Thus, for years with high disease pressure, a full prophylactic fungicide programme with fungicide applications at GS30/31, GS32 and GS55 may be necessary to protect yield potential in autumn-sown oats, particularly for disease-sensitive varieties such as Barra.
In such years, trials around the country have shown consistently big responses to the use of fungicides on oats, with some of the new SDHI chemistry showing considerable benefits over older chemistry in terms of yield and quality.
For spring-sown crops, two fungicide applications may be sufficient, although much will depend on the timing of infection. However, in years with low disease pressure, the yield potential can be delivered with a lower number of fungicide applications.
In such years, protective mildewicides such as Talius may have a role in preventing subsequent mildew infections. However, very frequent use of such fungicides will increase the risk of resistance development to these active ingredients in the mildew population.
Where disease pressure is present but not severe, UK research on oats has shown that reduced fungicide rates can be as effective as full rates.
Variety choice also has a role in disease control, particularly for mildew, as the varieties on the current spring and winter recommended lists have similar resistance to crown rust.
In a spring oat trial conducted in Oak Park in 2017, with high levels of mildew but low levels of rust, yields of Binary were reduced by 18% but yields of Barra were reduced by 38% when no fungicide was applied.
Some growers may be restricted in their choice of variety by their contract and may have to use a variety with lower disease resistance. With such varieties, closer monitoring of disease pressure will be needed in order to ensure that the optimal fungicide strategy is employed to maximise yield potential.
There are a number of potential diseases that can attack oat crops, but mildew and crown rust tend to be the most damaging.Research has not always found a benefit from fungicide application.Oat plants are very prone to blotching and purple discolouration, but this is not always a yield issue. 
This is a subscriber-only article
SHARING OPTIONS: